Battery grid

ABSTRACT

An expanded metal battery grid and process for making same which grid has a supporting border comprising a thermoplastic ribbon folded lengthwise around the grid&#39;s edge and ultrasonically bonded to itself through interstices in the grid.

This is a continuation of application Ser. No. 344,130 filed on Jan. 29,1982, now abandoned, which itself is a continuation of application Ser.No. 179,806 filed Aug. 20, 1980, now abandoned.

FIELD OF THE INVENTION

This invention relates to grids for supporting the active materials ofelectric storage batteries and more particularly to grids made frombilaterally expanded grid-making stock.

U.S. patent Daniels et al U.S. Pat. No. 3,853,626 discloses a continuousin-line process for making bilateral lengths of lead-acid storagebattery grid-making stock having an unexpanded strip at the longitudinalcenter of the stock, two reticulated grid wire networks expandedlaterally from the unexpanded center strip and unexpanded metal stripsat the distal edges of the grid wire networks remote from the centerstrip. The grid's current collecting header is formed from the centerstrip and is typically the grid's top border. The unexpanded distal edgestrips ultimately form the supporting border of the grid and istypically the grid's bottom border. More specifically, the Daniels et alprocess advances a narrow lead strip (i.e., about 1 mm thick)longitudinally between two rows of dies and reciprocating cutters whichconverge in incremental steps toward the longitudinal center of thestrip. The cutters shear wire-like segments from the longitudinal edgesof the strip to expand the strip laterally into two networks ofinterconnected segments extending outwardly in opposite directions fromthe center strip. The wire-like segments define a plurality ofdiamond-shaped interstices for retaining the battery's pasty activematerial. The thusly expanded strip is thereafter flattened to yield agrid of the type described in Wheadon et al U.S. Pat. No. 3,881,952. Thegrid wire networks are subsequently filled with battery reactant (e.g.as by belt pasting) and finally cut into individual battery plates.

The integral metal bottom border of grids so formed serves: to evenlydistribute the weight of the plate over the entire bottom edge of thegrid; to support the finished plate atop the mud ribs of a batterycontainer, when such ribs are provided; to retain the active material inthe bottom interstices of the grid adjacent the border; and to preventthe grid wires from puncturing battery's microporous separators, at thebottom folds thereof, in the case of separator-enveloped plates.Unfortunately, such metal borders add significantly to both the weightand cost of the grid.

It is an object of this invention to provide a relatively light-weight,low cost expanded metal battery grid for supporting the active materialof a storage battery by substituting a folded, spot-welded thermoplasticborder for the metal border typically used heretofore.

It is a further object of this invention to provide a process for makingsuch a grid from continuous lengths of bilaterally expanded grid-makingstock by enfolding the lateral edges thereof in a thermoplastic ribbonand subsequently spot welded the ribbon to itself through openings inthe stocks.

These and other objects and advantages of the present invention willbecome more readily apparent from the detailed description thereof whichfollows:

BRIEF DESCRIPTION OF THE INVENTION

The present invention comprehends an expanded metal grid for supportingthe active material of an electric storage battery wherein the gridincludes: a metal current collecting header along one edge (e.g. the topedge) thereof; a network of conductive grid wires extending from theheader throughout the major extent of the grid and such as to define aplurality of diamond shaped interstices therebetween for receiving thebattery's active material; a succession of grid wire loops defining asecond, scallopped edge of said network remote from the header edge; anda border comprising thermoplastic ribbon folded lengthwise about thescallopped edge such that the wings of the fold sandwich the edge loopstherebetween. Preferably, the expanded grid-wire network is formed bythe bilateral expansion process of Daniels et al and the border-formingplastic ribbons (i.e. one for each lateral network) are each foldedabout, and secured to, the scallopped edges of the grid-making stock ina continuous operation. In this regard, the plastic ribbon is foldedlengthwise and the edge of the grid-wire network inserted into thethusly formed crease such that the wings of the folded ribbon straddlethe scalloped edge. The wings are thereafter ultrasonically spot-weldedtogether through the diamond-shaped interstices along the edge of thegrid.

The folded border of the present invention provides all of the benefitsof the integral metal border and more. Vibration tests indicate theplates made from grids having plastic borders tend to retain theiractive materials longer than grids made with metal bottom borders.Apparently the plastic border cushions the plates base and therebyprolongs the retention of the active material. Moreover the plasticribbon at the edge of the grid reduces the possibility of internalshorting due to treeing around the edge of the battery separator orthrough any cracks therein at the bottom folds of typicalseparator-enveloped plates. The plastic border of the present inventionprovides the above-mentioned advantages and all with significant weightand cost reductions.

Process-wise a substantially flat plastic ribbon is fed toward acontinuous length of expanded grid-making stock, and caused tocontinuously enfold the lateral edges of the stock. In this regard, athree-sided plow including a funnel-like entrance of converging anglingsurfaces receives both the plastic ribbon and the edge of the expandedstock such as to progressively gently fold the ribbon lengthwise aboutthe edges of the stock. Following the plow, the two wing-like portionsof the ribbon straddling the edge are ultrasonically welded to eachother at a plurality of sites between the interstices of the grid-wirenetwork to secure the ribbon to the edge of the grid.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of an expanded metal storage battery grid inaccordance with the present invention;

FIG. 2 is an enlarged, perspective, partially broken away view of thefolded plastic ribbon border of FIG. 1;

FIG. 3 depicts a partially sectioned front elevational view of apparatusfor folding the plastic ribbon in accordance with the process of thepresent invention;

FIG. 4 is a partially sectioned partial bottom view of the apparatus ofFIG. 3 taken in the direction 4--4 thereof;

FIG. 5 is an enlarged sectioned side elevational view taken in thedirection 5--5 of FIG. 4; and,

FIG. 6 is an enlarged sectioned side view of the plastic ribbon taken inthe direction 6--6 of FIG. 4.

FIGS. 1 and 2 illustrate a preferred embodiment and show anexpanded-metal-type lead acid storage battery grid 2 having a currentcollecting header 4, and a plurality of grid wires 6 integral therewith.The grid wires 6 form the paste-retaining network of the grid and definea plurality of diamond-shaped interstices 8. A succession of grid wireloops 9 define a scallopped edge 10 at the bottom of the grid. Athermoplastic ribbon 12 is folded lengthwise about the scallopped edge10 so as to provide two wings 13, one on each side of the grid wirenetwork at the edge 10. The wings 13 are fused together at a pluralityof welds 14 spaced apart along the ribbon 12 and between the severalinterstices 8 at the edge 10. The header 4 includes a lug 16 forelectrically joining the grid 2 to similar grids in a battery cell.

FIGS. 3 and 4 depict the preferred process for enfolding edge 10 of grid2 in a thermoplastic ribbon 12. A flat thermoplastic ribbon 12 is fedfrom a reel (not shown) toward the advancing strip of expanded metalgrid-making stock 7. The ribbon 12 first passes into the nip of a pairof coacting rollers 18 having blades 20 on the peripheries thereof. Theblades 20 score center line of the ribbon 12 as best shown at 22 in FIG.6. Scoring the ribbon 12 facilitates folding of the ribbon 12 at thelongitudinal center thereof. In the alternative, of course, prescoredribbons could be used hence obviating the need for rollers 18 adjacentthe production line. As illustrated the scored ribbon 12 next passesover idler roller 24 to bring the ribbon 12 into substantial alignmentwith the edge 10 of the grid stock 7 entering the folding station. Inmany installations the idler roller 24 could be eliminated and theribbon 12 fed directly to the folding station from the reel.

The distal edge 10 of the grid stock 7 and the ribbon 12 converge at aplow 26. The plow 26 includes a top guide plate 28, a bottom guide plate30 and a fold guide plate 32 bolted together, as illustrated. The topand bottom guide plates 28 and 30 have angled surfaces 34 and 36respectively to gently cam the otherwise flat ribbon 12 entering theplow 26 into a U-fold about the distal edge 10 of the grid-making stock7 entering the plow 26. Similarly the fold guide plate 32 has an anglingsurface 38 which urges the fold 40 of the ribbon 12 toward the edge 10of the grid-making stock near the exit of the plow 26 (see FIG. 5).

Immediately following the folding station (i.e. plow 26) the ribbonstraddled edge 10 enters a welding station 42 where the wings 13 of theribbon 12 are fused together at a plurality of spaced apart weld sites14. The welding station 42 includes a continuously vibrating ultrasonichorn 44 and a rotating wheel 46 carrying a plurality of welding tips 48on the periphery thereof. The wheel 46 rotates at a rate commensuratewith the lineal speed of the grid-making stock 7. The welding tips 48are spaced about the periphery of wheel 46 so as to coincide with theinterstices 8 along the edge 10 of the grid-making stock 7 and serve topress the wings 13 together against the underside of the horn 44 to fusethe wings 13 together through the interstices 8.

Virtually any ultrasonically weldable thermoplastic material can be usedfor the border. Polypropylene homo- and co-polymers (e.g. withpolyethylene) are preferred for their strength, cost and readyworkability.

In one specific example the plastic border 12 comprises a polypropyleneribbon about 13 mm wide by about 0.25 mm thick. The ribbon straddles thegrid wire network such that the wings thereof extend up the sides of thenetwork from the bottom edge about 6 mm and are fused together atintervals through the interstices by welds which are approximately 1.7mm in diameter. The weld-making ultrasonic horn vibrates at a frequencyof about 20,000 cycles per second.

While this invention has been disclosed primarily in terms of forming abottom plastic border it is to be appreciated that the border may belocated on any of the grid's edges. Further though the invention hasbeen illustrated in terms of specific embodiments thereof it is notintended to be limited thereto but rather only to the extent set forthin the claims which follow.

The embodiments of the invention in which an exclusive property orprivilege is claimed is defined as follows:
 1. A substantially planargrid for supporting the active material of an electric storage batterycomprising: a conductive current collecting header along a first edge ofsaid grid; a network of conductive wires extending from said headerthroughout the major extent of said grid, said wires defining aplurality of interstices for receiving said active material and forminga scalloped second edge opposite said first edge; a thin, flexible,thermoplastic ribbon enclosing said scalloped edge, said ribbon beingfolded lengthwise about said scalloped edge so as to provide alongitudinal crease in said ribbon extending along the periphery of thegrid opposite said header and two wing-like ribbon portions divergingfrom said crease on opposite sides of said network and sandwiching saidscalloped edge therebetween; and a plurality of spot welds in saidribbon portions and extending through said interstices along said secondedge for joining said portions one to the other therethrough and therebysecuring said folded ribbon to said scalloped edge.
 2. A grid forsupporting the active material of an electric storage battery comprisinga conductive current collecting header along a first edge of said grid,a network of conductive wires extending from said header throughout themajor extent of said grid and defined in part by a scalloped second edgeopposite said first edge, said wires defining a plurality of intersticesfor receiving said active material, and a thermoplastic border enfoldingsaid scalloped edge, said border comprising a plastic ribbon foldedalong its longitudinal axis and having two wings disposed on oppositesides of said network, said wings being spot-welded one to the other ata plurality of sites through said interstices along said scalloped edge.